1. Field of the Invention
This invention pertains to an electrical contact apparatus and more particularly to an electrical contact apparatus for high-amperage current, which is particularly suitable for testing batteries.
2. Description of the Related Art
U.S. Pat. No. 5,966,014, which issued to Zhang et al. and which is incorporated by reference, describes an apparatus, a system and a method for testing a plurality of batteries for multiple operating specifications (“the '014 patent). The '014 patent describes how a number of batteries can be loaded into trays and positioned between appropriate probes or contact assemblies for testing the batteries simultaneously. Firm contact is preferably made at a consistent location on the batteries, which is typically on a centerline axis for cylindrical batteries. The centerline axis is best to assure that there is no variation from battery to battery resultant from the point of contact by the probe assembly. High-quality, sure and certain contact should be obtained at both ends of each battery for an electric current that is required to be drawn from each battery for test purposes. A second probe assembly, preferably concentrically arranged, is used to test the cell voltage of the batteries. The voltage contact does not require the current-handling capability of the amperage or current probe. The '014 patent describes an apparatus that operates both the current and voltage probes in a manner such that they are properly aligned so that they contact jointly one terminal of a battery and provide a current signal and a voltage signal. The other terminal contacts or connects with a current return probe. The terminals are at opposite ends of a cylindrical battery, and the current and voltage probes are aligned so that they move vertically along a common line of travel.
The '014 patent describes a tray into which ten, one hundred or any number of batteries can be loaded for testing. The tray and a number of additional trays can be loaded into an electrical cabinet for testing all of the batteries. Each battery tray is loaded remote from the cabinet and is then inserted and captured between lower and upper contact assemblies. A cam can be rotated to move the battery tray into operative contact with the lower and upper contact assemblies. The lower contact assembly is constructed with a bottom plate that is aligned above and is raised by cam action. The lower contact assembly is guided so that a number of upstanding components on the top of it are properly aligned for movement into operative contact between voltage and current contacts and the batteries in the tray. The system is constructed so that there are separate current flow paths and separate voltage contacts for each particular battery undergoing tests. The current flow path is structurally heavy duty in comparison to the gauge or weight of metal in the voltage contacts. The current flowing in the voltage contacts is relatively small, but it is sufficient to provide an adequate voltage signal. The current flow rates differ by several orders of magnitude. The current in the voltage contacts may be in the microampere range.
The electrical cabinet described in the '014 patent includes an adjustable voltage and current power supply, which is connected at a selected terminal to form an output current that is applied to the batteries. The output of the power supply is measured by a volt meter connected to the power supply. The volt meter forms a measurement of the output or terminal voltage, which is recorded. Another volt meter measures the terminal voltage across the batteries. A battery circuit is formed, and current is directed through a load resistor. The current is measured and recorded. The current may have a transient start and then a steady state aspect. And after a period of time, it will also have a decay curve as the battery heats and the resistance changes as a result of internal resistance in the battery. A timing cycle for taking the sample takes these factors into account. At a given instant, the circuit is closed and made operative so that current flows through the load resistor. A signal is measured and recorded at a related time interval after the circuit is closed, which provides a measurement of battery current flow. Other parameters of the batteries can be measured in a similar fashion. Please review the '014 patent for additional information.
An important aspect of a battery testing machine is the electrical connection between a battery being tested and the electrical circuitry in the machine. U.S. Pat. No. 5,903,154 issued to Zhang et al, and is incorporated by reference (“the '154 patent”). The '154 patent addressed this issue and discloses a battery test contact assembly. Battery testing involves substantial current flows. The current flow is provided through a test circuit, which provides a load for the battery and a current source. Batteries are tested for quality by providing timed charging current and discharge current in typical tests. The quality of the electrical connection between the battery being tested and the electrical circuitry in the machine is affected by a spring force of a spring that forces a battery contact against a battery terminal. If the contact force is outside a desired range, false readings may be obtained because the contact is not sufficient to enable full current flow between the battery terminal and the battery contact.
The '154 patent disclosed a battery tester contact assembly having a pair of parallel upper and lower printed circuit boards (PCBs) spaced from one another by a set of typically four conductor rods. The conductor rods provide parallel current conductor paths. The spacing between the PCBs is adjustable to accommodate batteries of different lengths. The upper PCB has a connector, which has two terminals that connect to electrical test circuitry in the battery testing machine. The test circuitry provides a controlled resistance across the battery, which may range from very large to nearly zero so that the current flow can be tested. The test circuitry will typically include an ammeter. The test circuitry typically also features a current source to impose a charging current on the battery, which is especially important in testing rechargeable batteries. It may be necessary to test a rechargeable battery by providing a controlled discharge through a low resistance and then applying a charging current to the cell.
The PCBs can be rectangular, and the lower PCB is connected to the upper PCB by four electrically conductive rods located near the corners of the PCBs. The rods extend up through the lower PCB and are electrically connected to the lower PCB, preferably using solder to make the connections. The four rods are connected in parallel and have a common circuit connection through conductive material on each side of the lower PCB. The rods serve two purposes, namely electrical conduction and spacing between the upper and lower PCBs. The rods are preferably made of a quality conducting metal, such as copper or a copper alloy. The rods are fixed to the lower PCB, but are slidingly and electrically engaged with the upper PCB. The upper PCB has electrically conductive metal sleeves that are in electrical contact with a conductive material on the upper PCB and that receive the rods in a manner that allows movement to vary the spacing between the upper and lower PCBs and that ensure a good and reliable electrical connections between the rods and the sleeves and the upper PCB. The upper and lower PCBs have electrical contacts for engaging opposing terminals of cylindrical batteries. Other configurations are described in the '154 patent for batteries having a different shape.
The electrical contacts on the PCBs that engage the batteries preferably include a voltage probe located in the center of the positive terminal contact. When including a voltage probe, it is desirable to have two leads or conductors out of the positive battery terminal. One is obtained by a large footprint contact area against the positive battery terminal so that the current flow is directed through that. A second contact point to the positive terminal provides terminal voltage output through an appropriate conductor. A concentric construction can be used to provide two contacts, one with large surface area and the other with small surface area. Two conductors are used in the movable contact assembly, with one carrying the current and the other providing a voltage signal. Voltage is generally measured using an independent point of contact with the battery terminal in order to have a separate signal path for voltage measurements. Battery testing normally involves substantial momentary current flows through the current flow path connected with the battery. In contrast, the signal path for voltage measurements involves a small current flow, typically 1 microampere or less, depending on the quality and nature of the voltage measuring circuit. FIGS. 4A, 4B and 5 in the '014 patent and the description of those figures show how separate voltage and current flow paths were achieved in battery testing according to the '014 and '154 patents (U.S. Pat. Nos. 5,966,014 and 5,903,154, respectively). Please review the '014 and '154 patents for additional information.
The contact assembly of the '154 patent provided appropriate contact to the battery through the use of a movable contact. That movable contact came into abutting contact with the battery terminal at a plurality of tines or prongs. For most low current applications, the tine contact structure provides adequate contact between the terminal and the contact. For high current applications, however, such as for example 100 amps or higher, such a contact presents a high resistance to current flow between the terminal and the contact, resulting in high temperatures, which is undesirable. U.S. Pat. No. 7,614,907, which was issued to Zhang and which is incorporated by reference, discloses a contact terminal with a self-adjusting contact surface that is suitable for high current applications (“the '907 patent”). The self-adjusting contact includes a plurality of conductive fibers, such as wires, that provide sufficient contact with a battery terminal for high current flow. However, the self-adjusting contact of the '907 patent does not provide a separate voltage probe. Consequently, there is a need for an improved battery testing machine or apparatus, a battery test contact assembly and/or a battery test contact that provides a current flow path and a separate voltage measurement, which is preferably particularly well-suited for high current flow.